In recent years, with the rapid spread of the Internet, there has been demand for a larger capacity, upgrading, and cost-effectiveness of an optical access system. Research on PON has proceeded as a technique for implementing such a system. PON is a cost-effective optical access communication system in which a plurality of users can share a transmission path between a center device and an optical passive element by an optical passive element such as an optical power splitter accommodating a plurality of transmission paths from the plurality of users in a single transmission path.
At present, in Japan, there is introducing a cost-effective optical access communication system GE-PON (Gigabit Ethernet (registered trademark)-PON) in which up to 32 users share 1 Gbps class line capacity according to time division multiplexing (TDM). Thereby, a fiber-to-the-home (FTTH) service has been provided to the users at a practical fee and spread rapidly.
Meanwhile, research on a 10 G-Ethernet passive optical network (EPON) of 10 Gbps class has proceeded as a next generation optical access system capable of coping with the needs for larger capacity and IEEE standardization thereof was completed in 2009. This scheme provides a system capable of increasing the capacity while using the same GE-PON as the existing one for a transmission path portion due to an increase in a bit rate of a light transceiver. Also, a larger capacity beyond 10 Gbps class may be required according to a service such as a high-definition video service. However, further speeding up of the bit rate of the transceiver (40 or 100 Gbps class) leads to a significant increase in cost of the transceiver and there is a problem in that a system is not practical.
As means for cost-effectively implementing large capacity, a wavelength tunable wavelength division multiplexing (WDM)/TDM-PON in which wavelength tunability is given to a light transceiver so that the number of light transceivers within a station-side device can be gradually increased in accordance with a bandwidth requirement and in which TDM and WDM are combined has been reported (for example, see Non-Patent Document 1). FIG. 1 is a configuration diagram showing the wavelength tunable WDM/TDM-PON.
The WDM/TDM-PON system requires a light transceiver having wavelength tunability for a subscriber device or a station-side device. As is known, a light receiver for the wavelength tunable WDM/TDM-PON can configure a wavelength tunable receiver by demultiplexing wavelength-multiplexed N-wave signal light for each wave with a wavelength filter and then selecting and receiving an electrical signal corresponding to signal light having a desired wavelength in an electric switch after a photodiode (PD) corresponding to each wavelength photoelectrically converts signal light into an electrical signal (for example, Patent Document 1).